Sitting in the window seat of a passenger plane, it’s easy — and often necessary, if you’re a nervous flyer — to ignore the roar of the turbojet engines. Yet an incredible amount of engineering goes into making these machines powerful, efficient and safe.
The fan of a jet engine draws in just a fraction of the air bypassing the engine core, but it’s more than enough. A compressor and a series of blades squeeze the air before it reaches the combustor, where fuel is injected and ignited. The resulting hot gases spin the turbine, turning thermal energy into mechanical energy. Turbine exhaust and fan airflow are what propel the average Boeing 747 to speeds upwards of 550 mph.
Let’s look at the four components that allow modern aircraft to generate thrust and achieve liftoff.
Fan blades are most often constructed from titanium or steel, but some — like the ones designed exclusively for Boeing’s 777X and its GE9X engines — are made from carbon-fiber composite. Composite blades are created digitally using computer-aided design (CAD). During manufacturing, hundreds of layers of carbon fiber and epoxy form the blades. Heat and pressure are applied to toughen the material, and a leading edge — most often titanium — is the finishing touch that protects the blade from harm, including damage caused by unsuspecting geese. A unique combination of form and function, a composite blade from a GE90-115b was acquired by The Museum of Modern Art in 2004.
A compressor blade begins its life as a single metal pellet. A ceramic layer prevents the pellet from oxidizing as it’s heated in an oven at 980 degrees Celsius. The resulting slug is then placed in a lubricated forming dye, where a press applies one thousand metric tons of pressure. The newly formed blade is cooled in water, cleaned of metal burrs and once more coated in a protective ceramic layer before being placed in a convection oven. Tempering compressor blades ultimately allows them to suck in 2,600 pounds of air per second.
The blade takes its final shape after a press applies 1,600 metric tons of pressure. Glass (a byproduct of heating the ceramic layer) and excess metal are removed. Finally, a protective cast protects the blade while a broaching machine carves a dovetail, which will allow the blade to be slotted into the shaft of the engine. The cast is removed, and what remains is a finished compressor blade.
Combustion chambers are traditionally manufactured over a period of five to eight months. This lengthy process entails cutting, welding and polishing sheets of temperature-resistant metal alloys. Thanks to additive design (AD) and additive manufacturing (AM), however, combustion chamber manufacturing and the whole of the aerospace industry are accelerating into an exciting new direction. Rather than subtracting material, like a sculptor chipping away at a block of marble, engineers can now add material by 3D printing combustion chambers in a one-step process known as selective laser melting. Using CAD and selective laser melting, engineers are able to reduce emissions, costs and delivery times.
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Located in the hottest and fastest-moving section of a jet engine, turbine blades must be able to stand up to temperatures in excess of 1,200 degrees Celsius. The first turbine blade prototypes were made from steel, but they underperformed due to the high temperatures reached during flight. Today, turbine blades are made of a single crystal of nickel alloy that can fit in the palm of your hand.
To cast turbine blades, wax is injected around a ceramic core to form the shape of the blade. Cooling channels formed by the ceramic core will allow the blades to operate in environments hotter than their melting point. The assembly is then coated in layers of slurry to form a ceramic shell. Heat is applied to strengthen the shell and melt away the wax, leaving a cavity in the shape of the blade. Molten metal is poured into the finished mold, and a furnace keeps the metal molten until the casting is ready to be removed, cooled and solidified. Careful control of external temperatures helps ensure that the casting forms into a single crystal of metal with temperature-tolerant microstructures.
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We’ve only scratched the surface of the engineering innovations that go into the manufacture and assembly of jet engine components. Before an engine can be affixed to the wing of a plane, engineers must overcome a myriad of challenges ranging from creep to thermal stress.
Problems arising during the design, analysis and production of products will always be present in the field of mechanical engineering. That’s why UT Austin offers two 100% online mechanical engineering programs: the Master of Science in Mechanical Engineering and the Mechanical Engineering Controls Graduate Certificate. Both of our professional programs are designed to help professionals find innovative solutions to engineering-related problems.
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